Review of effects of shock (<60 kbar; <6x109 Pa) on magnetism of lunar samples

Abstract

Experimental shock studies of highland and mare soils in the range of a few to 50 kbar (5 x 109 Pa) have given the following results: (1) Shock, if less than 20 kbar, does not change the magnetic characteristics of the soil substantially and only weak and unstable shock remanence is generated in a field of 0.5 Oe. (2) Shock of between 20 and 50 kbar lithifies the soil and gives rise to stable shock remanence. Acquisition is approximately linear in field for a given shock level. At 30 kbar the acquisition parameter for the highland soil was 10-5 G cm3 g-1 Oe-1. In this range of 20-50 kbar the products of shock are petrologically and magnetically similar to certain regolith breccias. (3) Shock demagnetization preferentially demagnetizes the softer part of thermoremanent magnetization (t.r.m.) and hence makes it relatively harder. The significance of these results is that shock remanence is likely to be the cause of the natural remanent magnetization (n.r.m.) of certain regolith breccias and shock may modify the primary remanence of other samples.